The present invention relates to an ultrasound inspection apparatus that generates an ultrasound image to be used in the inspection and diagnosis of an inspection object by capturing an image of the inspection object such as an organ inside a living body by transmitting and receiving an ultrasonic beam, and relates to an ultrasound inspection method and a recording medium.
Conventionally in the medical field, ultrasound inspection apparatuses such as ultrasound image diagnostic apparatuses that utilize ultrasound images have been put to practical use. In general, such an ultrasound inspection apparatus includes an ultrasound probe having a plurality of elements (ultrasound transducers) built therein and an apparatus main body connected to this ultrasound probe. The ultrasound inspection apparatus generates an ultrasound image by transmitting ultrasonic beams toward an inspection object (subject) from the plurality of elements of the ultrasound probe, receiving ultrasonic echoes from the subject with the ultrasound probe and then electrically processing the received ultrasonic echo signals in the apparatus main body.
When an ultrasound image is generated in such an ultrasound inspection apparatus, ultrasonic beams are focused and transmitted from the plurality of elements of the probe onto an inspection region of the subject such as an organ inside a living body or a lesion inside that organ, and ultrasonic echoes from reflectors of the inspection region such as the surfaces and boundaries of the organ or lesion are received via the plurality of elements. However, because ultrasonic echoes reflected by the same reflector are received by a plurality of elements, compared to an ultrasonic echo signal that is reflected by a reflector positioned at the focal position of an ultrasonic beam transmitted from a transmission element and received by the transmission element, an ultrasonic echo signal that is reflected by the same reflector and received by another element different to the transmission element is delayed. Consequently, in an ultrasound inspection apparatus, ultrasonic echo signals received by the plurality of elements are subjected to analog-to-digital (A/D) conversion to form a piece of element data, and then the piece of element data is subjected to reception focus processing, that is, the piece of element data is subjected to delay correction to match the phase of the element data and to phasing addition to generate sound ray signals, and then an ultrasound image is generated on the basis of the thus-obtained sound ray signals.
In such an ultrasound inspection technology, in order to improve the image quality of an ultrasound image, signals obtained by transmitting a plurality of ultrasonic beams that converge at a plurality of different focal points have been added together and as a result the quality of signals has been improved from the past.
For example, JP 2009-240700 A discloses an ultrasound diagnostic apparatus in which a virtual point sound source is formed by causing transmission ultrasonic waves emitted from a plurality of transducer elements that make up a transmission transducer element group to converge at a transmission convergence point, and then reception ultrasound waves reflected from a plurality of continuous observation points as a result of the transmission ultrasonic waves emitted from this point sound source are received by a plurality of transducer elements that make up a reception transducer element group, and reception phasing addition is performed on obtained reception signals for the number of channels such that an observation point becomes a reception convergence point. In addition, in this ultrasound diagnostic apparatus, the same reception phasing addition is also performed on reception signals obtained using the reception transducer element group and each transmission transducer element group sequentially shifted in the direction of the array of the transducer elements, and transmission phasing addition is performed on the post-reception phasing addition reception signals to correct a transmission delay caused by the difference in propagation distance from each transmission convergence point to the observation point.
In the ultrasound diagnostic apparatus disclosed in JP 2009-240700 A, reception phasing addition and transmission phasing addition are performed on reception signals obtained from a plurality of transducer elements, and as a result, a transmission beam and a reception beam having a substantially uniformly fine beam width with respect to a depth direction of the subject can be formed with high precision and high sensitivity. Thus, JP 2009-240700 A discloses an ultrasound diagnostic apparatus that can generate and display image data that is excellent in terms of spatial resolution, contrast resolution and an S/N ratio (signal-noise ratio).
In particular, in JP 2009-240700 A (refer to the working example illustrated in FIG. 5 therein), as illustrated in FIG. 8, it is indicated that when the focuses of three transmission transducer element groups are converged at respective transmission convergence points (hereinafter, referred to as focal points) Ft1 to Ft3 and each focal point is regarded as a virtual point sound source (hereinafter, referred to as a virtual point sound source), reflection waves obtained as a result of wave fronts from each virtual point sound source being reflected at the position of the same observation point (reflection point) Px are received by the reception transducer element group. In JP 2009-240700 A, it is thereby assumed that signal quality can be improved from the past by adding together signals transmitted through a plurality of different focal points with respect to one point.